1. Field of the Invention
The present invention relates to the a control unit for a synchronous engaging device that is provided in a transmission, and in particular, it relates to a control unit that can detect the degree of damage when a gear whine occurs to the synchronous engaging device.
2. Description of the Related Art
As a transmission installed in a vehicle, there is a multi-step transmission equipped with an input shaft to which driving force of a driving source such as a motor is input, an output shaft which is arranged in parallel with the input shaft, one or more input gears (or shift gears), being provided on the input shaft, for transmitting rotation of the input shaft, and one or more output gears (or shift gears), being provided on the output shaft, for meshing with each of the one or more input gears. Also, such a transmission is provided with a synchronous engaging device (or a synchronizer device) for synchronizing and engaging the rotation of the input gear or the output gear with the rotation of the input shaft or the output shaft. This synchronous engaging device has a synchronizing sleeve that can be stroked in the axial direction between the engaging position in which the input gear or the output gear engages with the input shaft or the output shaft and the release position in which the engagement is released.
In the synchronous engaging device as described above, due to the functional decline of a synchronizer ring, a synchronous engagement operation is not completed even when the stroke position of the synchronizing sleeve is in the position in which the synchronous engagement operation should be essentially completed, but instead differential rotation speed occurs between the rotational speed of the input side and the rotational speed of the output side. In this condition, when a tip of dog tooth of the synchronous sleeve and a tip of dog tooth of the shift gear come in contact, an abnormal noise such as a metal frictional sound or a clattering sound occurs between them because of relative rotation. In this specification, the state in which such an abnormal noise occurs is referred to as gear whine state. If the synchronous engagement operation is performed continuously and repeatedly in the gear whine state, it may eventually lead to the damage of each parts of the synchronous engaging device (such as shift forks, dog tooth, hub sleeves, etc.).
The existence of gear whine has conventionally been determined by differential rotation speed in accordance with stroke position of the synchronizing sleeve. In other words, in the shift control unit described in Japanese Patent Application Publication No. 2006-153235 (Patent Document 1), when it is detected that the sleeve has reached the mesh starting position where it begins to mesh with an idling gear and when the relative rotational speed between the input shaft and the output shaft does not fall within the synchronization decision value that determines the completion of synchronization, it is determined that a gear whine has occurred. Moreover, in the shift control unit described in Japanese Patent Application Publication No. 2002-71005 (Patent Document 2), when the relative rotational speed between an input rotational speed and an output rotational speed is equal to or more than a predetermined value and the amount of displacement of the sleeve is equal to or more than a predetermined value, it is determined that a gear whine has occurred.
Furthermore, the conventional technologies described in Patent Documents 1 and 2 take measures to prevent further damages to the mechanical structure of the synchronous engaging device after and while determining gear whine. The shift control unit described in Patent Document 1 does not immediately disable the gear position which has generated a gear whine, but uses the gear position while suppressing the gear whine by changing the control method of engagement operation so as to reduce damage caused to the transmission. The shift control unit disclosed in Patent Document 2, when it is determined that gear whine has occurred more frequently than a predetermined number in a specific gear position, identifies the gear position as gear whine position, whereas performing shift control by skipping the gear whine position.